Automotive vehicles have used catalytic converters to treat unburned hydrocarbons, carbon monoxide and various nitrogen oxides produced from the combustion of hydrocarbon fuels in the engine. The engine exhaust gases flow through a catalytic converter that contains a very small quantity of noble metal catalysts such as palladium, platinum and rhodium coated on the surface of ceramic substrate inside the catalytic converter. The hydrocarbon and oxide constituents are oxidized and/or reduced by these catalysts.
A challenge often encountered in preparing exhaust treatment catalysts for catalytic converters lies in making the most efficient use of the relatively expensive noble metals. The noble metals must be distributed in the catalytic converter in such a manner that all of the metal is exposed to exhaust gas flowing through the converter. Due to heat and vibration, the precious noble metal particles have a tendency to agglomerate and grow over time to form larger crystalline particles with reduced conversion efficiency. Thus, it is necessary to incorporate a sufficient excess quantity of the noble metals onto the surface of ceramic substrate inside the catalytic converter to ensure continuous catalytic activity over the lifetime of the vehicle.
The cost of emission control systems could be reduced if the optimum dispersion of platinum group metals (PGM) nanoparticles can be achieved. It is also important to maintain optimum dispersion of the noble metals on the surface of ceramic substrate inside catalytic converter surfaces over time. For automotive applications, it would be much easier to maintain optimum dispersion of the PGM nanoparticles over the vehicle lifetime if the temperature of catalytic converters can be controlled to within a maximum temperature range of typically about 500˜650 degrees C. This requires the use of additional mechanisms to control the maximum converter temperature, which can reach temperatures of up to 1,000 degrees C. under some operating conditions if not controlled.
Accordingly, a method and apparatus are needed to maintain the temperature of a catalytic converter within an optimal temperature range in order to prolong the lifetime of the catalytic converter, which would lead to significant cost reduction.